System and method for diagnostic of low pressure exhaust gas recirculation system and adapting of measurement devices

ABSTRACT

A system for a diesel engine having an intake manifold and an exhaust manifold comprises a turbocharger between the intake and exhaust manifolds of the engine, a low pressure exhaust gas recirculation system, and a high pressure exhaust gas recirculation system. Further, the system includes a controller for coordinating adjustment of exhaust gas recirculation valves and throttles in the system to compensate for interaction between the high and low pressure exhaust gas recirculation systems.

The present application is a continuation of U.S. patent applicationSer. No. 11/460,704, titled “System and Method for Diagnostic of LowPressure Exhaust Gas Recirculation System and Adapting of MeasurementDevices”, filed Jul. 28, 2006, which claims priority to U.S. ProvisionalPatent Application No. 60/711,198, titled “Method and Apparatus toControl Low Pressure EGR”, filed Aug. 25, 2005.

The present application is also a continuation of U.S. patentapplication Ser. No. 11/245,630, titled “System and Method for HighPressure and Low Pressure Exhaust gas Recirculation Control andEstimation”, filed Oct. 6, 2005.

The entire contents of each are incorporated herein by reference intheir entirety for all purposes.

BACKGROUND AND SUMMARY

Diesel engines may use re-ingested burnt exhaust gases to increase fueleconomy and reduce emissions. For example, an exhaust gas recirculation(EGR) system may be used to recirculate exhaust gases from the exhaustmanifold to the intake manifold. Such operation can displace fresh airand lower oxygen concentration in the cylinder, as well as reduceformation of NOx during combustion.

In some engine configurations that have a turbocharger, both a lowpressure and high pressure EGR system may be used. For example, a highpressure (HP) EGR loop from the exhaust manifold (upstream of theturbine of turbocharger) to the intake manifold (downstream of thecompressor of the turbocharger), may be used. In addition, a lowpressure (LP) loop from downstream of the turbine to upstream of thecompressor may also be used. See, for example, U.S. Pat. No. 6,820,599.

The inventors herein have recognized several disadvantages with such anapproach. Specifically, in some engine configurations, a mass airflow(MAF) sensor may be installed to estimate or measure flows in the HP EGRand LP EGR loops. However, over time, the sensor may degrade or age,thus reducing the ability to accurately control the HP and/or LP EGR.Further, when both EGR systems are active, a reading from the MAF sensorcan be biased because interactions between the two EGR systems. As such,degraded estimation, and thus control, of the HP and LP EGR systems canresult.

At least some of the above issues may be addressed by a system for adiesel engine having an intake manifold and an exhaust manifold,comprising: a turbocharger between the intake and exhaust manifolds ofthe engine; a low pressure exhaust gas recirculation system with a firstend coupled to the exhaust manifold downstream of the turbocharger and asecond end couple to the intake manifold upstream of the turbocharger,said low pressure exhaust gas recirculation having a first valve coupledthereto for regulating flow; a high pressure exhaust gas recirculationsystem with a first end coupled to the exhaust manifold upstream of theturbocharger and a second end coupled to the intake manifold downstreamof the turbocharger, said high pressure exhaust gas recirculation havinga second valve coupled thereto for regulating flow; a first mass airflowsensor coupled in the engine intake manifold upstream of said second endof said low pressure exhaust gas recirculation system; and a controlsystem configured to diagnose the degradation of said first mass airflowsensor. In this way, it is possible to identify degraded operation ofthe sensor and take corrective action, if necessary.

Several different diagnostic strategies can be used to detect thedegradation of the MAF sensor. In one particular example, the diagnosticstrategy of the MAF sensor may be based on information from a second MAFsensor. In another example, an intrusive strategy may be used wheresystem operation is purposely adjusted to enable improved diagnosis ofthe MAF sensor under selected conditions. In yet another example,conditions may be opportunistically identified under which improveddiagnostics may be performed, such as when a low pressure EGR valve isclosed, for example.

In this way, the degradation of a MAF sensor can be diagnosed so thatthe control of dual EGR system may be monitored to improve robustnessand/or durability.

In another embodiment, the disclosed approaches can make it possible todetect leakages or blockages of the low pressure EGR loop, and thusdegradation of an EGR system can be provided.

In yet another example, a control system can provided which adapts todegradation of a MAF sensor, such as an aging effect. In this way, theEGR flows in the dual EGR system can be more accurately controlled evenin the presence of sensor degradation. Thus, it is possible to providerobust control of both EGR systems by providing accurate estimation ofEGR flow via adaptation of degraded MAF sensor performance.

DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic view of a compression ignition engine systemhaving an EGR system and a VGT;

FIGS. 2-3 are high level flowcharts of example operation.

FIG. 4 is an example flowchart of a first diagnostic method for a massair flow (MAF) sensor in an exhaust gas recirculation (EGR) system witha high pressure EGR loop and a low pressure EGR loop.

FIG. 5 is an overview of the diagnostic method described in FIG. 4.

FIG. 6 is an example flowchart of a second diagnostic method for a MAFsensor in an EGR system with a high pressure EGR loop and a low pressureEGR loop.

FIG. 7 shows the change of low pressure EGR valve position with time toillustrate the diagnostic method described in FIG. 6.

FIG. 8 shows the change of expected MAF and measured MAF with time toillustrate the diagnostic method described in FIG. 6.

FIG. 9 is an overview of the diagnostic method described in FIG. 6.

FIG. 10 is an example flowchart of the third diagnostic method for a MAFsensor in an EGR system with a high pressure EGR loop and a low pressureEGR loop.

FIG. 11 is an overview of the diagnostic method described in FIG. 10.

FIG. 12 is an overview of a fourth diagnostic method for a MAF sensor inan EGR system with a high pressure EGR loop and a low pressure EGR loop.

FIG. 13 is an example flowchart of a method to detect leakages orblockages in the manifold of the low pressure EGR loop.

FIG. 14 is an example flowchart of one embodiment of a method for MAFsensor adaptation.

FIG. 15 is an example flowchart of another embodiment of a method forMAF sensor adaptation.

DETAILED DESCRIPTION

Turning first to FIG. 1, there is shown a simplified schematic diagramof a compression ignition engine system 10 equipped with a high pressureand low pressure exhaust gas recirculation (EGR) system (12 and 13,respectively) and a variable geometry turbocharger (VGT) 14. Arepresentative engine block 16 is shown having four combustion chambers18, although more or fewer cylinders may be used if desired. Each of thecombustion chambers 18 includes a direct-injection fuel injector 20. Theduty cycle of the fuel injectors 20 is determined by the engine controlunit (ECU) 24 and transmitted along signal line 22. Air enters thecombustion chambers 18 through the intake manifold 26, and combustiongases are exhausted through the exhaust manifold 28 in the direction ofarrow 30.

To reduce the level of NOx emissions, the engine is equipped with an EGRsystem. The EGR system includes a high pressure (HP) EGR system 12,which comprises a conduit 32 connecting the exhaust manifold 28 to theintake manifold 26. This allows a portion of the exhaust gases to becirculated from the exhaust manifold 28 to the intake manifold 26 in thedirection of arrow 31. A HP EGR valve 34 regulates the amount of exhaustgas recirculated from the exhaust manifold 28. The valve 34 may be athrottle plate, pintle-orifice, slide valve, or any other type ofvariable valve. Further, a low pressure (LP) EGR system 13 is shown,which includes a conduit 33 connecting gases from the output of theturbocharger turbine (discussed below) to the inlet of the turbochargercompressor. This allows a portion of the exhaust gases to be circulatedfrom the exhaust to the intake upstream of the turbocharger system, andthus at lower pressures. A LP EGR valve 76, similar to valve 34, may beused to regulate the flow of LP EGR. Each of valves 34 and 76 may becontrolled by ECU 24.

In the combustion chambers, the recirculated exhaust gas acts as aninert gas, thus lowering the flame and in-cylinder gas temperature anddecreasing the formation of NOx. On the other hand, the recirculatedexhaust gas displaces fresh air (thus decreasing oxygen content) andreduces the air-to-fuel ratio of the in-cylinder mixture which, up to alimit, may contribute toward lowering NOx production.

Turbocharger 14 uses exhaust gas energy to increase the mass of the aircharge delivered to the engine combustion chambers 18. The exhaust gasflowing in the direction of arrow 30 drives the turbocharger 14. Thislarger mass of air can be burned with a larger quantity of fuel,resulting in more torque and power as compared to naturally aspirated,non-turbocharged engines.

The turbocharger 14 includes a compressor 36 and a turbine 38 coupled bya common shaft 40. The exhaust gas 30 drives the turbine 38 which drivesthe compressor 36 which, in turn, compresses ambient air 42 (and LP EGRgas, if present) and directs it (arrow 43) into the intake manifold 26.The VGT 14 can be modified as a function of engine speed during engineoperation by varying the turbine flow area and the angle at which theexhaust gas 30 is directed at the turbine blades. This is accomplishedby changing the angle of the inlet guide vanes 44 on the turbine 38. Theoperating position for the engine guide vanes 44 is determined from thedesired engine operating characteristics at various engine speeds andloads by ECU 24.

Between turbine 38 and the LP EGR system 13 may be an emission controlsystem 74, which may include one or more emission control devices, suchas a particulate filter, oxidation catalyst, selective catalyticreduction catalyst, NOx trap, or combinations thereof. Furtheradditional devices may be included upstream of turbine 38 and/ordownstream of system 74. In one embodiment, one or more pressure and/ortemperature sensors may be coupled in system 74, and used to adjustengine operation.

As can be appreciated from FIG. 1, both EGR systems 12 and 13 and theVGT 14 regulate gas flow from the exhaust manifold 28. The effect of theEGR and VGT is, therefore, jointly dependent upon the conditions in theexhaust manifold 28. EGR flows and fresh air flows may also be regulatedby adjusting either the high pressure EGR throttle 84 or the lowpressure EGR throttle 78, which are both controlled by ECU 24.

All of the engine systems, including the EGR systems 12 and 13, VGT 14,throttle valves 78 and 84, and fuel injectors 20 are controlled by theECU. For example, signal 46 from the ECU 24 regulates the HP EGR valveposition, and signal 48 regulates the position of the VGT guide vanes44.

In the ECU 24, the command signals 46, 48 to the EGR system 12 and VGT14 actuators, as well as other command signals, are calculated frommeasured variables and engine operating parameters. Sensors andcalibratable lookup tables provide the ECU 24 with engine operatinginformation. For example, manifold absolute pressure (MAP) sensor 50provides a signal 52 to the ECU 24 indicative of the pressure in theintake manifold 26 downstream of the HP EGR entrance and pressure sensor96 provides a signal 98 indicative of pressure upstream of the HP EGRentrance in the intake manifold. Likewise, exhaust manifold pressure(EXMP) sensor 54 provides an EXMP signal 56 to the ECU 24 indicative ofthe pressure in the exhaust manifold 28 upstream of the HP EGR exit.Further, an air charge temperature sensor 58 provides a signal 60 to theECU 24 indicative of the temperature of the intake air charge 42. Afirst mass airflow (MAF1) sensor 80 and a second mass airflow (MAF2)sensor 64 also provide signals 82 and 66 respectively indicative of therespective airflows in the intake system to the ECU 24. While FIG. 1shows sensor 80 in the intake manifold upstream of the LP EGR inlet andupstream of throttle 78, it may also be located downstream of thethrottle, for example. Further, while FIG. 1 shows sensor 64 in theintake manifold downstream of the LP EGR inlet and upstream of the HPEGR inlet and upstream of turbocharger 14, sensor 64 may also be locateddownstream of turbocharger 14 and either upstream or downstream ofthrottle 84, while still upstream of the HP EGR inlet.

Sensors may also provide information as to valve position for feedbackcontrol, such as for any or each of valves 34, 84, 76, and 78. Also,exhaust pressure in the LP EGR system may be provided by pressure sensor90 via signal 92. In addition, exhaust gas oxygen concentration, whichcan be indicative of air-fuel ratio, can be provided by oxygen sensor72. Additional sensory inputs can also be received by the ECU alongsignal line 62 such as engine coolant temperature, engine speed, andthrottle position. Additional operator inputs 68 are received alongsignal 70 such as acceleration pedal position. Based on the sensoryinputs and engine mapping data stored in memory, the ECU controls theEGR systems, throttles, and VGT to regulate the intake airflow,recirculated exhaust gases, and/or the intake manifold pressure (MAP)and controls injectors 20 to regulate fuel delivery.

Under some conditions, in order to reach a desired total EGR flow ratein the intake manifold at certain speeds and loads, one or both of theLP and HP EGR systems may be used. In other words, only the HP EGR loopis used under some conditions, only the LP EGR loop is used under otherconditions, and both loops are used under still other conditions.However, since EGR may take one or more paths under differentconditions, it can be difficult to determine an amount and compositionof, as well as control, a quantity of EGR flow in the intake manifold.

One example approach for estimation and control offers an improvedsolution for the control of low pressure EGR, and offers improvedaccuracy in transients and improved robustness in the face of noisefactors. This example utilizes a set of sensors that can provide anindication of both the LP and HP EGR mass flow. In this way, the flowsmay be independently identified and thus accurately controlled. In oneembodiment, a mass airflow sensor located upstream of the LP EGR inlet,along with additional flow and/or pressure sensors, may be used toadvantage in providing accurate estimation and control of low pressureand high pressure EGR flow.

Referring now to FIG. 2, a routine is described for controlling LP andHP EGR valves. In this example, the routine first determines in 210whether both high and low pressure EGR systems are active. If so, theroutine continues to 212 to determine the high pressure EGR flow. Thisflow can be estimated by determining the amount of flow entering adefined volume, such as the intake manifold from the entrance of the LPEGR system to the engine, the amount of flow exiting the volume, and anyflow compressibility in the volume. In one example, the flow exiting isthe flow entering the engine (W_eng), which can be calculated fromvolumetric efficiency (stored in the ECU as a function of speed andother engine operating parameters) and the manifold pressure (MAP) fromsensor 50. The flow entering can be determined from sensor 64 (MAF2), ifsuch a sensor is provided. In an alternative embodiment, the flowentering can be estimated from the pressure drop across throttle 84using an orifice flow equation.

Thus, in one approach, the following dynamic equation may be used todetermine the HP EGR flow (W_egr_hp):W_egr_(—) hp=d(m_int)/dt+W_eng−MAF2

where MAF2 is the flow measured by the MAF sensor downstream of the LPEGR valve and represents the sum of fresh air and LP EGR flows, W_eng isthe charge flow into the engine, and is calculated from volumetricefficiency and m_int is the estimated mass of gases in the intakemanifold based on the ideal gas law.

Next, in 214, the routine determines the LP EGR flow present which canbe determined based on the total flow upstream of the HP EGR inlet(e.g., MAF2) minus the flow entering the intake (e.g., 42 measured byMAF1). Alternatively, flow entering the intake may be estimated based onthe pressure values upstream and downstream of throttle 78 using anorifice flow equation, if desired.

Next, in 216, the routine determines the desired LP and HP EGR flowsbased on operating conditions, such as speed and load. Then, in 218, theroutine adjusts the LP and HP EGR valves (34, 90) based on comparing thedesired flows to the estimated or measured values. In one example, afeedback controller, such as a proportional or proportional-integral(PI) controller may be used, where the valve commands are determined as:Cmd_egr_(—) lp=PI(W_EGR_(—) lp−W_EGR_(—) lp_des(N, trq))Cmd_egr_(—) hp=PI(W_EGR_(—) hp−W_EGR_(—) hp_des(N, trq))

where Cmd_egr_lp/hp are the adjustments, or commanded duty cycle orpositions to the EGR valves, and W_EGR_lp/hp_des are the desired lowpressure and high pressure EGR flows, which may be a function of speed(N), torque (trq), load or other engine operating conditions.

If the answer to 210 is no, the routine continues to 220 to determinewhether the LP EGR system is active. If so, the routine continues to 222to determine the amount of LP EGR flow, such as using the calculationdescribed above in 214. Then, the routine continues to 224 to determinea desired LP EGR flow, and then adjust the LP EGR valve in 226 based onthe desired and estimated values, which may be done using a PIcontroller as described above.

If the answer to 220 is no, the routine continues to 228 to determinewhether the HP EGR system is active. If so, the routine continues to 230to determine the amount of HP EGR flow, such as using the calculationdescribed above in 212. Then, the routine continues to 232 to determinea desired HP EGR flow, and then adjust the HP EGR valve in 234 based onthe desired and estimated values, which may be done using a PIcontroller as described above.

If the answer to 228 is no, the routine closes both LP and HP EGRvalves, and moves the throttles to a desired value based on operatingconditions.

In this way, it is possible to provide independent and accurate controlof the EGR systems by providing an accurate estimate and/or measurementof the LP and HP EGR flows. Specifically, in an embodiment using a massairflow sensor upstream of the LP EGR inlet (and optionally using asecond mass airflow sensor downstream of the LP EGR inlet), accuratedetermination of the LP EGR flow and thus accurate control of EGR may beachieved.

While FIG. 2 shows one example embodiment for controlling and estimatingEGR flows, an alternative embodiment is described in FIG. 3. In theexample of FIG. 3, coordinated control of multiple EGR valves andthrottle valves is provided to provide accurate control even undervarying or transient operating conditions.

Specifically, FIG. 3 shows an alternative embodiment that may be usedwhen both LP and HP EGR flow is active. In 310-312, the routinedetermines values of the HP and LP EGR flows, and then determinesdesired HP and LP EGR flows in 314, similar to that shown with regard to212-216 discussed above. Then, in 316, the routine determines whetherthe pressure differential across the LP EGR system is greater than athreshold minimum value. The threshold value may be variable, forexample, it may be an amount to give a desired flow at maximum LP EGRvalve position, which can be a function of operating conditions,temperature, etc. Alternatively, a fixed threshold may be used, or theroutine can determine whether the LP EGR valve is open greater than athreshold amount slightly less than maximum position.

If the answer to 316 is yes, the routine continues to 318 to adjustoperation of (e.g., close) the LP throttle 78 to increase a vacuum inthe air pipe upstream of the compressor side of the turbocharger 14. Inone example, if the pressure drop across the LP EGR valve is notsufficient, a larger pressure drop can be generated by throttling thegas upstream of the low pressure intake. In one embodiment, a singlecontrol command may be used to achieve a larger range of LP EGR flow byusing the following control structure carried out in 320 and 322:Cmd _(—) egr _(—) lp=PI(W_EGR_(—) lp−W_EGR_(—) lp_des(N, trq))Cmd _(—) egrvv _(—) lp=min(1, cmd _(—) egr _(—) lp)Cmd _(—) egrthr _(—) lp=max(0, cmd_egr_(—) lp−1)

where N is engine speed, trq is desired torque, min (1, cmd egr. Ip)is aMinimum function. 1 is a unitless representation of maximum valveposition,and max(0,crnd egr Ip-1) is a maximum function.

A similar approach can then be taken for the HP EGR system ifinsufficient flow is obtained as determined at 324. For example, in326-330, the following structure may be used:Cmd _(—) egr _(—) hp=PI(W_EGR_(—) hp _(—) W_EGR_(—) hp_des(N, trq))Cmd _(—) egrvv _(—) hp=min(1, cmd _(—) egr _(—) hp)Cmd _(—) egrthr _(—) hp=max(0, cmd _(—) egr _(—) hp−1)

Continuing with FIG. 3, if the answer to 324 is no, the routinecontinues to 334 to adjust the LP and HP EGR valve positions to achievethe desired flow as noted above with regard to 218.

While the above example adjusts EGR and/or throttle valve positions toobtain desired HP and LP EGR flows that are a function of conditionssuch as speed and load, other control objectives may be used. Forexample, the routine can adjust set points, or desired values, of HP andLP EGR flows to achieve a desired intake manifold temperature,T_int_des(N,trq), which is itself a function of engine operatingconditions. For example:W_EGR_(—) hp_des=W_EGR_(—) hp_des_(—) ff+PI(T_int−T_int_des(N.trq))W_EGR_(—) lp_des=W_EGR_(—) lp_des_(—) ff−PI(T_int−T_int_des(N.trq))

where W_EGR_hp/lp_des_ff is the initial desired hp/lp EGR flow, whichmay be based on speed and load, for example.

In this way, it is possible to adjust HP and LP EGR flows, while alsocontrolling intake manifold temperature, for example. Such operation maybe used to advantage in achieving a desired cylinder charge temperaturefor low temperature homogenous charge compression ignition combustion,where the temperature rise of compression causes ignition rather thanthe injection timing of diesel fuel. Still other advantages may beachieved in that by controlling intake manifold temperature, exhausttemperature may be affected.

In still another alternative embodiment, the routine can control a LP/HPEGR fraction. In other words, the ratio of the EGR flows may be adjustedto vary during operating conditions, and be controlled via coordinatedadjustment of the EGR and/or throttle valves as:X _(—) egr _(—) lp=W _(—) egr _(—) lp/W_engX _(—) egr _(—) hp=W _(—) egr _(—) hp/W_eng

where X_egr_lp is the fraction of LP EGR flow, and X_egr_hp is thefraction of HP EGR flow. These values can then be controlled via the PIcontroller discussed above with regard to FIGS. 2 and/or 3. Further,intake manifold temperature control may also be included, if desired.

In yet another alternative embodiment, the routine can further includecontrol of a burnt gas fraction. For example, using an exhaust lambdasensor (e.g., 72) the routine can estimate the burnt gas fraction in theLP and HP EGR flows and control the LP/HP burnt gas fractions in theintake manifold. In this example, additional sensor information may beused, such as the temperature in the intake manifold (58).

Specifically, the fraction of inert gas in the intake manifold (f_man)is discriminated into the fraction coming from the low pressure loop(f_man_lp) and the fraction of inert gas coming from the high pressureloop (f_man_hp). Each of these fractions is observed based on thepreviously described sensors and the specific space velocity of each EGRloop. These observers, which may be responsive to the lambda sensor andtemperature sensor, allow an accurate estimation of the re circulatedgas composition.

In one approach, the following differential equations may be used tomodel variations of the fraction in the intake manifold of inert gascoming from low pressure EGR loop and high pressure EGR loop,respectively:d(f_man_(—) lp)/dt=[(Fegrlp*(MAF2−MAF1)−f_man_(—) lp*(MAF2+W _(—) egr_(—) hp)]/Mmand(f_man_(—) hp)/dt=[(Fegrhp−f_man_(—) hp)*W _(—) egr _(—) hp−f_man_(—)hp*MAF2]/Mman

where Fman is the fraction of EGR gas in the manifold, f_man_lp is thefraction of EGR gas in the intake manifold coming from the low pressureEGR loop; f_man_hp is the fraction of egr gas in the intake manifoldcoming from the high pressure EGR loop; Mman is the mass of gas in themanifold volume, f_egr_lp is the fraction of EGR gas at the outlet ofthe EGR low pressure manifold (which may be approximated by inversionthe measured lambda value in the exhaust pipe with an additionaltransport delay which is specific to the LP EGR loop), f_egr_hp is thefraction of EGR gas at the outlet of the EGR high pressure manifold(which can be approximated by the inversion of the measured lambda valuein the exhaust pipe with an additional transport delay which is specificto the HP EGR loop), and noting that Fman equals the combination off_man_hp and f_man_lp, W_egrp equals the difference between MAF2 andMAF1, and W_egr_hp equals the difference between W_eng and MAF2.

A double control of the f_man_lp and f_man_hp may be so performed, viatheir respective valves, in a de-correlated way to achieve the desiredfraction of inert gas in the intake manifold within bandwidthconstraints as imposed by each loop and their interaction with enginecycle dynamic time scales. Further improvement in the robustness of thecontrol may be achieved with the use of the lambda sensor though a moreaccurate knowledge of the composition of the re-circulated gases.

More precisely desired values for the fraction of high and low pressureEGR (_man_lp_des and f_man_hp_des) can be determined from a singledesired fraction as:f_man_(—) lp_des=k*f_man_desf_man_(—) hp_des=(1−k)*f_man_desSo that f_man_des=f_man_(—) hp_des+f_man_(—) lp_des

where f_man_des is the desired total fraction of burnt gas in the intakemanifold, f_man_lp_des is the desired fraction of burnt gases in theintake manifold coming from the low pressure loop, f_man_hp_des is thedesired fraction of burnt gases in the intake manifold coming from thehigh pressure loop, and k is an element of [0;1] and is the weight whichdetermines the transfer of effort from one EGR loop to the other.

In other words, as k increases, f_man_lp_des increases, fman_hp_desdecreases, and thus a higher fraction of burnt gases in the intakemanifold is requested to from the low pressure EGR loop and vice versa.The determination of k at the engine conditions allows a betterscheduling of the use of the EGR loops based on their specificconstraints. The parameter k may be varied as a function of any numberof operating conditions, such as, for example, engine temperature,speed, load etc to satisfy some predetermined (or instantaneouslyestablished) set of constraints on the intake charge composition and ortemperature as the case may be.

Control of inert gas fractions can also be combined with the coordinatedcontrol of the EGR valves and throttle valves, and intake chargetemperature control, if desired. Further, as noted below herein,compensation for transport delays may also be included.

As noted above herein, various measurement locations for flows may beused. In one example, since the EGR and/or mass flows are measuredupstream of the intake manifold, it may be possible to compensate forflow delays in the low pressure EGR flow by estimating the transportdelay between the LP EGR inlet and intake manifold and the high pressureEGR by estimating transport delay between HP EGR inlet and intakemanifold. The transport delays may be estimated by dividing the pipevolume by a volumetric flow speed based on a representative density.Then, the routine can compensate for the flow delays by adjusting thedesired flow amounts.

To perform the control methods and systems described above, in someembodiments, a mass air flow sensor such the MAF1 sensor 80 in FIG. 1may be used to determine the flow-rate in the low pressure EGR manifold.Thus, a diagnostic strategy for the MAF1 sensor 80 may be used toimprove the robustness of the control methods and systems. FIG. 4 is anexample flowchart of a first example diagnostic method for a mass airflow sensor in an exhaust gas recirculation (EGR) system with a highpressure EGR loop and a low pressure EGR loop. In this example, thediagnostic of the MAF1 sensor may be based on a measured MAF signal fromanother MAF sensor and estimated values.

The routine first determines in 410 if the diagnosis of the MAF1 sensorbased on estimation is enabled. If so, the routine continues to 420 toestimate the low pressure EGR flow. The estimation can be based on adelta pressure across the low pressure EGR loop, which is the differencebetween the pressure at the inlet of the low pressure EGR loop(P_inlet_lp_egr) and the pressure at the outlet of the low pressure EGRloop (P_outlet_lp_egr). The estimation of the delta pressure across thelow pressure EGR loop may be based on physical principles ofthermodynamics such as mass conservation and standard orifice flowequation, for example. Using these principles, the flow of low pressureEGR may be estimated based on information from sensors commonlyinstalled in an engine, such as exhaust back pressure sensor (upstreamturbine, pressure sensor 54), intake manifold pressure sensor (MAPsensor), MAF2 sensors and VGT position.

The orifice flow equation for the low pressure EGR loop provides therelationship between flow, pressure drop, and geometrical considerations(such as EGR valve cross section A_lp_egrv):W _(—) egr _(—) lp=f ₀(A _(—) lp _(—) egrv, P_inlet_(—) lp _(—) egr,P_outlet_(—) lp _(—) egr)*Rho _(—) lp _(—) egrwhere Rho_lp_egr is the massic density of the low pressure EGR gases.

When P_inlet_lp_egr can be assumed as the pressure downstream of anemission control device such as 74 in FIG. 1 (P_down_dpf) andP_outlet_lp_egr can be assumed as the pressure upstream compressor(P_up_comp), the above equation becomes:W _(—) egr _(—) lp_estimated=v(A _(—) lp _(—) egrv, P_down_(—) dpf,P_up_comp)*Rho _(—) lp _(—) egrSo, an estimation of Rho_lp_egr, P_down_dpf and P_up_comp is used forthe estimation of W_egr_lp.

Several approximations may be used to estimate P_down_dpf, P_up_comp,and Rho_lp_egr. First, a P_down_dpf approximation may be estimated usingmass conservation and standard orifice flow equation across turbine 38as below:Wexh=W_massfuel+MAF2=u(W_massfuel, MAF2)Wexh=f(VGTpos, Pexh_upturbine, Pexh_downturbine).

Thus, the exhaust pressure downstream of the turbine, Pexh_downturbine,is a function of VGT position (or a cross sectional area of the flowpassing through the turbine), the exhaust pressure upstream of theturbine, Pexh_upturbine, and exhaust flow as shown below:Pexh_downturbine=g(Wexh, VGTpos, Pexh_upturbine) orPexh_downturbine=h(u(W_massfuel, MAF2), VGTpos, Pexh_upturbine)

In some embodiments, emission control devices such as diesel particulatefilter, oxidation catalyst, selective catalytic reduction catalyst, NOxtrap, or combinations may be disposed downstream of the exhaust pipe orin the low pressure EGR loop. Thus, the estimation of the pressuredownstream of the emission control device (P_downdpf) is used, which canbe calculated as below:P_downdpf=P _(—) updpf−DeltaPdpf

where DeltaPdpf is the pressure drop across the emission control deviceand P_updpf is the pressure upstream the emission control device, inthis example the DPF. P_updpf can be estimated by a model based on gasviscosity and exhaust flow as below:P _(—) updpf=Pexh_downturbine+z(viscosity, W _(—) exh).

In one approach, DeltaPdpf may be determined by a delta pressure sensor.In another approach, an estimation of the soot load and other enginevariables or events such as diesel filter regeneration or catalyticconverter operation may be used to estimate the pressure across theemission control device. Thus, the pressure downstream of the emissioncontrol device may be estimated as:P_downdpf=h(u(W_massfuel, MAF2), VGTpos, Pexh_upturbine)+z(viscosity, W_(—) exh)−DeltaP _(—) dpf.

Second, the approximation of P_up_comp may be estimated using standardorifice flow equation across compressor 36 as below:MAF2=f ₂(Compressor_cross_section, P_up_comp,P_intake_manifold)*Rho_up_compressorwhere Compressor_cross_section is the cross sectional area through whichgases pass in the compressor; and Rho_up_compressor is the mass densityof the gas passing the compressor 36 and P_intake_manifold is thepressure downstream of compressor or the intake manifold pressure (MAP)of the engine. In one approach, Rho_up_compressor can be estimated basedon speed density relationship upstream of the compressor. The aboveequation can be rearranged into:P_up_comp=g(MAF2, T_up_compressor, P_up_comp, Compressor_cross_section,P_intake_manifold).

In some embodiments, since a usual speed density sensor, such as MAFsensor (also called T_MAF), may provide information on the temperature,the temperature T_up_comp may be available through this sensor. In otherembodiment, T_up_comp may be determined by a model.

Third, the approximation of Rho_lp_egr may be estimated using the idealgas law as below:Rho _(—) lp _(—) egr=P_up_comp/(R*T _(—) lp _(—) egr).

The temperature of low pressure EGR gas T_lp_egr may be determined invarious ways. In one approach, T_lp_egr can be estimated based on heattransfer equation and temperature sensor measured from the two MAFsensors upstream and downstream low pressure EGR inlet. In anotherapproach, T_lp_egr can be determined by a model based on engine setpoint or other temperature sensors.

Using the three approximations described above, the flow of low pressureEGR can be estimated as:W _(—) egr _(—) lp_estimated=v(A _(—) lp _(—) egrv, g(MAF2,T_up_compressor, P_up_comp, Compressor_cross_section,P_intake_manifold), (u(W_massfuel, MAF2), VGTpos,Pexh_upturbine)+z(viscosity, W _(—) exh)−DeltaP_dpf)*Rho _(—) lp _(—)egr.

Alternatively, the flow of low pressure EGR may be estimated as afunction of variable engine operating parameters:W _(—) egr _(—) lp_estimated=f(tqi, n, T _(—) dpf, deltaPdpf, w _(—)exh, dpf _(—) regen events)

where tqi is indicated torque, n is the speed of the engine anddpf_regen events is the regeneration events of a diesel particulatefilter or a catalyst converter.

Now continuing to 430, the routine measures the low pressure EGR flowusing the MAF2 and MAF1 sensors at specific engine conditions. Themeasured low pressure EGR flow can be determined based on the total flowupstream of the high pressure EGR inlet (MAF2) minus the flow enteringthe intake of the low pressure EGR (e.g., MAF1). Next, the routine, in440, compares the estimated flow with the measured flow to determine thedeviation. Then, the routine, in 450, determines if the deviation isoutside of a predetermined range. If so, the routine, in 460, determinesthat the MAF1 sensor is degraded. In this way, it is possible to provideaccurate degradation detection of the MAF1 sensor.

FIG. 5 is an overview of the diagnostic method and system described inFIG. 4. The diagnostic system may comprise an estimator 510 whereinformation from engine sensors are used. Information may include flowmeasured by the MAF2 sensor, fuel mass flow, exhaust flow, temperatureupstream of compressor, pressures upstream of compressor, intakemanifold pressure, exhaust pressure upstream of turbine, pressure dropacross an emission control device disposed in the low pressure EGR loop,low pressure EGR valve cross section area, compressor cross sectionarea, VGT opening position, viscosity, etc. The system may also comprisea estimator where the measured flow of low pressure EGR loop isdetermined based on flows measured by MAF1 and MAF2. Another estimatormay be used to compare the estimated flow with measured flow and theninput the deviation into a diagnostic logic. In the diagnostic logic 520of the system, deviation and engine's conditions are analyzed todiagnose the MAF1 sensor's status.

FIG. 6 is an example flowchart of a second diagnostic method for a MAFsensor in an EGR system with a high pressure EGR loop and a low pressureEGR loop. An intrusive strategy is used in this diagnostic approach. Theroutine first, in 610, determines if diagnostics of the MAF1 sensorbased on an intrusive strategy is enabled. Such intrusive monitoring maybe disabled under conditions where the intrusive action may causeoperation noticed by the driver, for example.

If the intrusive diagnostic is enabled, the routine continues to 620 toperform a predetermined small perturbation of low pressure EGR valveposition. Next, the routine, in 630, measures the flow passing throughthe MAF1 sensor. Then, the routine, in 640, determines the deviation ofmeasured value from the expected value. Next, the routine, in 650,determines if the deviation is greater than a threshold. If the answeris no, the routine goes back to 610. If the answer is yes, the routine,in 660, determines that MAF1 sensor is degraded.

One example of an intrusive strategy is illustrated in FIG. 7 where thechange of low pressure EGR valve position with time is shown. Thelpegrv_int_sp is the low pressure EGR valve intrusive setpoint.lpegrv_int_sp may also be a function of torque and engine speed or anyspecific engine conditions such as temperatures, engine states, etc.

FIG. 8 shows the change of expected flow and measured flow rate fromMAF1 sensor with time in response to the intrusive event illustrated inFIG. 7. Maf1_max_int_thr is the maximum threshold from which a positivedeviation between measured MAF1 (Meas_MAF1) and expected MAF (Exp_MAF1)is taken into account. Maf1_min_int_thr is the minimum threshold fromwhich a negative deviation between measured MAF1 and expected MAF1 istaken into account. T1, T2, delay_time_1, delay_time_2 are functions oftorque and engine speed or related to some engine's conditions orengine's events.

The MAF deviation detection may be illustrated in one intrusive eventshown in the FIGS. 7 and 8 where the low pressure EGR valve intrusivesetpoint is set to lpegrv_int_sp during T2−T1. At time t element ofT=[T1+delay_time_1; T2+delay_time_2], at k discrete element of [0; N]where this interval represents the discretisation of the time intervalT, if (Meas_MAF1<MAF1_min_int_thr or Meas_MAF1>MAF1_max_int_thr), then:

d(k) = Meas_MAF 1(k) − Exp_MAF 1(k)${Average\_ d} = \frac{\sum\limits_{k = 0}^{k = N}{d(k)}}{N}$

Average_d represents the average value of the deviation during oneintrusive event. Average_d may be used to determine if the MAF1 sensoris functioning at an acceptable level. Alternatively, several thresholdcriterions may be used to detect if the MAF1 sensor is degraded. Thecriterions may include inverted behavior of the MAF sensor, offsetdeviation, measure stuck to a value, and degradation of the timeresponse.

In another approach, Average_d may be averaged over the number ofintrusive events to determine an aging tendency of the MAF1 sensor. Thisstrategy can identify the MAF1 sensor as a non functional devicedepending on detection of deviation over the time of use.

In this way, it is possible to utilize the response of the low pressureEGR system to monitoring functionality to isolate degradation of theMAF1 sensor.

FIG. 9 is an overview of the diagnostic method and system described inFIG. 6. At intrusive event, low pressure EGR valve position,LP_EGR_position is set which corresponds to an expected MAF1 flow value,MAF1_EXPECTED, which are input into the estimator 910. The diagnosticmethod also includes an intrusive deviation calculation 920 where theexpected MAF1 value from estimator 910 and measured MAF11 value areinput and analyzed to determine a MAF1_deviation. In one embodiment, anintrusive event may be introduced into intrusive deviation calculation920. The output from intrusive deviation calculation 920 is a measureddeviation, MAF1_INT_DEV_MEASURED.

FIG. 10 is an example flowchart of the third diagnostic method for a MAFsensor in an EGR system with a high pressure EGR loop and a low pressureEGR loop. First, the routine, in 1010, determines if the diagnostic forthe MAF1 sensor based on an opportunistic offset detection is enabled.If so, the routine, in 1020, determines if the low pressure EGR valve isclosed during a time period of T2−T1. If the answer is no, the routineends. If the answer is yes, the routine, in 1030, determines an offsetdeviation of the MAF1 sensor based on the measure of the MAF2 sensor.Next, the routine, in 1040, determines if the deviation is out of apredetermined range. If so, the routine, in 1050, determines that MAF1sensor is degraded.

In the example above, the diagnostic approach is based on opportunistoffset detection. At certain engine conditions, the low pressure EGRvalve may not be used and stay closed. In these situations, the flowpassing through the MAF1 sensor (sensor 80 for example) should be thesubstantially same as the flow passing through the MAF2 sensor (sensor60 for example). Assuming that the MAF2 sensor provides an accuratereading and can be considered as a reference, an offset deviation or adegraded response time may be detected if the MAF 1 sensor is degradedwhen the low pressure EGR valve is closed.

In one approach, considering some engine conditions and the situationwhere the low pressure EGR valve stays closed during a time T2−T1, for telement of [T1;T2], the deviation may be defined as:d=MAF1(t)−MAF2(t+transport_delay)

where transport_delay can be defined as a function of MAF2(t), thetemperature upstream compressor and pressure downstream compressor.Alternatively, the transport_delay may be defined as function of tqi andengine speed.

Further, using this approach, the deviation in steady state may beidentified where there is no more need to evaluate the transport delay.

FIG. 11 is an overview of diagnostic method and method described in FIG.10. The diagnostic strategy includes a calculator where the measuredflows from MAF2 and MAF1 sensors are calculated to determine thedeviation. Then, the results are input into deviation calculation 1100where deviation of the MAF1 sensor is analyzed based on the deviationbetween MAF2 and MAF1 sensor at the condition where the low pressure EGRvalve is closed.

FIG. 12 is an overview of a fourth diagnostic method and system for aMAF sensor in an EGR system with a high pressure EGR loop and a lowpressure EGR loop. This strategy combines each of the three approachesdescribed above. For example, the diagnostic calculation 1260 mayreceive a MAF1_DEV_ESTIMATED after input data are processed by theestimator 1210 based on the first embodiment (estimation strategy)described above associated with FIGS. 4 and 5. The diagnosticcalculation 1260 may also receive a MAF1-DEV_INT_ESTIMATED after inputdata are processed by the estimator 1240 and intrusive deviationcalculation 1250 based on the second embodiment (intrusive strategy)described above associated with FIGS. 6, 7, 8 and 9. Additionally, thediagnostic calculation 1260 may receive a MAF1_DEV_MEASURED after theinput data are processed by the opportunist deviation calculation 1230based the third embodiment (opportunist offset detection) describedabove associated with FIGS. 10 and 11. The diagnostic strategy mayanalyze the deviations based on priorities and logical combinations. Forexample, an average of each method may be used, or the methods may beused sequentially. In this way, it is possible to determine the type ofdeviation of the MAF1 sensor and thus improves the accuracy of thediagnostic.

The diagnostic strategies described above are advantageous for theoperation of the EGR flows in a diesel engine with a dual EGR loopsystem. For example, undesired emission level due to an overflow orunderflow of the low pressure EGR gases may be estimated through thediagnostic, and then corrected or reduced by disabling one or both ofthe high pressure and low pressure EGR systems, for example.

FIG. 13 is an example flowchart of a method to detect leakages orblockages in the manifold of the low pressure EGR loop. The routineassumes that the MAF1 and MAF2 sensors are properly functioning. Thedetection and estimation of the leakage or blockage is performed basedon a comparison between the measure of the flow through the low pressureEGR manifold (MAF2-MAF1) and an estimator of the low pressure EGR flow.First, the routine, in 1310, estimates the flow of the low pressure EGRmanifold. The estimation may be performed by incorporating informationfrom the sensors on an engine to physical models or a map. One exampleof the estimation has been described above in association with FIG. 4.In one embodiment, the flow of the low pressure EGR manifold may beestimated based on delta pressure across the LP EGR loop based onthermodynamics and information from sensors such as exhaust backpressure sensor, intake manifold pressure sensor, MAF2 sensor and VGTposition. Next, the routine, in 1320, measures the flow of the lowpressure EGR manifold via MAF2 and MAF1 sensors. The flow of the lowpressure EGR manifold equals (MAF2-MAF1).

Next, the routine, in 1330, determines the deviation between theestimated flow and measured flow. The deviation W egr_lp_dev equalsaverage(W_egr_lp_estimation-(MAF2-MAF1)). At specific engine conditions,the deviation may correspond to either a leak or a blockage. Next, theroutine, in 1340, determines if the deviation is greater than zero. Ifso, the routine, in 1350, determines that there is a leakage in the lowpressure EGR manifold. The leakage creates a flow of exhaust gases inthe atmosphere. If the answer is no, the routine, in 1360, determinesthat there is a blockage in the low pressure EGR manifold.

In some embodiments, the amount of exhaust gas released in theatmosphere can be determined based on W_egr_lp_dev and the engineoperating conditions if desired. In other embodiments, the size of theorifice responsible for the leak can be determined. For example, theorifice flow equation and the pressure evaluation in the low pressuremanifold may be used to determine the size of the orifice. The pressureacross the low pressure manifold may be approximated with the pressuredownstream an emission control device if existed and the temperatureestimation along the low pressure EGR manifold.

In this way, the robustness of the hardware of the low pressure EGR loopcan be monitored, thus more accurate control of EGR may be achieved.

FIG. 14 is an example flowchart of one embodiment of a method ofadaptation of a MAF sensor. As described above, the control of the lowpressure EGR and the detection of the leakage or blockage may useinformation from the MAF1 and MAF2 sensors. However, the sensors may besubject to aging effects or slow variation over time. The routine 1400provides a strategy to adapt the MAF1 sensor assuming that MAF2 has beencorrectly adapted by other strategies, such as based on information froma fuel injector and air-fuel ratio sensor, for example. The routinefirst, in 1410, determines an estimate of the deviation of flow based onthe difference between estimated flow and measured flow in the lowpressure manifold. In one example, the deviation may be defined below:

W_egr_dev=W_egr_estimated-(MAF2-MAF1). In one embodiment, W_egr-dev maybe determined by the approach described above associated with FIG. 4.

Next, the routine, in 1420, adapts deviation at each favorable conditionto determine an adapted MAF1 value. In one example, adapted MAF1 may bedefined as:

MAF 1_adapted = MAF 1_corr + MAF 1${{{where}\mspace{14mu}{MAF}\; 1{\_ corr}} = {{W\_ egr}{{\_ dev}.\mspace{14mu}{Thus}}}},\begin{matrix}{{{W\_ egr}{\_ estimated}} = {{{W\_ egr}{\_ dev}} + \left( {{{MAF}\; 2} - {{MAF}\; 1}} \right)}} \\{= {{{- {MAF}}\; 1{\_ corr}} + \left( {{{MAF}\; 2} - {{MAF}\; 1}} \right)}} \\{= {{{MAF}\; 2} - \left( {{{MAF}\; 1} + {MAF1\_ corr}} \right)}} \\{= {{{MAF}\; 2} - {{MAF1\_ adapted}.}}}\end{matrix}$

As a consequence, any deviation between the estimation and the adaptedmeasure is reduced. MAF1_corr may be stored in a table function of MAF1measure and continuously adapted at each favorable condition.

FIG. 15 is an example flowchart of another method of adaptation for theMAF sensor. At specific speeds and loads, for example, the low pressureEGR valve may remain closed. If this condition is detected, the routine1500 may be used for adaptation of MAF1 assuming that MAF2 has beencorrectly adapted by other strategies. The routine first, in 1510,performs an opportunistic measure of MAF 2. It should be noted that theflow measured by MAF2 and MAF1 sensors should be the same when the lowpressure EGR valve is closed and there is no aging effect on MAF1. Theaging effects of MAF1 may be detected whenMAF2=MAF1+X(MAF2)

where X is the offset which may be related to aging effect of the MAF1sensor a MAF2 value.

Next, the routine, in 1520, determines an adapted value of MAF1 based onthe opportunistic measure of MAF2. The adapted MAF value may be definedas:MAF1_adapted=MAF2=MAF1+MAF1_(—) corr(MAF1).

Thus, MAF1_corr(MAF1)=MAF2−MAF1.

The values of MAF1_corr may be stored in a table which is a function ofMAF1. In one embodiment, MAF1_corr may be adapted at each opportunisticevent and used to determine the adapted value of MAF1. In anotherembodiment, the values of MAF1_corr may be interpolated (for a minimumof two opportunities events at different values for example), thus anadaptation of MAF1 may be performed for the whole range of MAF1.

In this way, it is possible to provide robust control of the EGR systemsby providing accurate estimation of EGR flow via adaptation of degradedperformance of a MAF sensor such as degradation due to aging of the MAFsensor.

Additionally, the diagnostics or adaptation strategies which arepresented herein for the MAF1 sensor and are based on a comparisonbetween the two MAF sensors can also be used for a diagnostic of theMAF2 sensor. In this approach, it is assumed that MAF1 sensor is readingaccurately or has been adapted, corrected or diagnosed by otherstrategies such as a comparison of MAF1 measure with the computedaspirated mass flow W_ENGINE, where W_ENGINE=f(Intake manifold Pressure,Intake manifold temperature, engine speed, volumetric_efficiency (enginespeed, intake manifold pressure)) when low pressure and high pressureEGR valves are closed intrusively or opportunistically.

Note that the control and estimation routines included herein can beused with various engine configurations, such as those described above.The specific routine described herein may represent one or more of anynumber of processing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various steps orfunctions illustrated may be performed in the sequence illustrated, inparallel, or in some cases omitted. Likewise, the order of processing isnot necessarily required to achieve the features and advantages of theexample embodiments described herein, but is provided for ease ofillustration and description. One or more of the illustrated steps orfunctions may be repeatedly performed depending on the particularstrategy being used. Further, the described steps may graphicallyrepresent code to be programmed into the computer readable storagemedium in controller 24.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and nonobvious combinationsand subcombinations of the various systems and configurations, and otherfeatures, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsubcombinations regarded as novel and nonobvious. These claims may referto “an” element or “a first” element or the equivalent thereof. Suchclaims should be understood to include incorporation of one or more suchelements, neither requiring nor excluding two or more such elements.Other combinations and subcombinations of the disclosed features,functions, elements, and/or properties may be claimed through amendmentof the present claims or through presentation of new claims in this or arelated application. Such claims, whether broader, narrower, equal, ordifferent in scope to the original claims, also are regarded as includedwithin the subject matter of the present disclosure.

1. A method for controlling a diesel engine having an intake system andan exhaust system, the engine further having a turbocharger coupledbetween the intake and exhaust systems of the engine, a low pressureexhaust gas recirculation system with a first end coupled to the exhaustsystem downstream of the turbocharger and a second end coupled to theintake system upstream of the turbocharger, said low pressure exhaustgas recirculation system having a first valve coupled thereto forregulating flow, a high pressure exhaust gas recirculation system with afirst end coupled to the exhaust system upstream of the turbocharger anda second end coupled to the intake system downstream of the turbochargersaid high pressure exhaust gas recirculation system having a secondvalve coupled thereto for regulating flow, a first throttle coupled inthe intake system between said second end of said high pressure exhaustgas recirculation system and said second end of said low pressureexhaust gas recirculation system, and a second throttle coupled upstreamof said second end of said low pressure exhaust gas recirculationsystem, the method comprising; coordinating adjustment of the first andsecond valves and first and second throttles, said coordinatingincluding: during a first condition: adjusting low pressure exhaust gasrecirculation flow by adjusting the first valve with the first throttlefully opened and adjusting high pressure exhaust gas recirculation flowby adjusting both the second valve and the second throttle, where saidfirst condition includes insufficient pressure in the high pressureexhaust gas recirculation system and sufficient pressure in the lowpressure exhaust gas recirculation system, where sufficient pressure inthe low pressure exhaust gas recirculation system includes at least whenpressure across the low pressure exhaust gas recirculation system isgreater than a first threshold, and where insufficient pressure in thehigh pressure exhaust gas recirculation system includes at least whenpressure across the high pressure exhaust gas recirculation system isless than a second threshold; during a second condition: adjusting lowpressure exhaust gas recirculation flow by adjusting the first valve andthe first throttle and adjusting high pressure exhaust gas recirculationflow by adjusting the second valve with the second throttle fullyopened, where said second condition includes sufficient pressure in thehigh pressure exhaust gas recirculation system and insufficient pressurein the low pressure exhaust gas recirculation system, where sufficientpressure in the high pressure exhaust gas recirculation system includesat least when pressure across the high pressure exhaust gasrecirculation system is greater than a first threshold, and whereinsufficient pressure in the low pressure exhaust gas recirculationsystem includes at least when pressure across the low pressure exhaustgas recirculation system is less than a second threshold; and during athird condition: adjusting low pressure exhaust gas recirculation flowby adjusting both the first valve and the first throttle and adjustinghigh pressure exhaust gas recirculation flow by adjusting both thesecond valve and the second throttle, where said third conditionincludes insufficient pressure in both the high and low pressure exhaustgas recirculation systems, where insufficient pressure in the highpressure exhaust gas recirculation system includes at least whenpressure across the high pressure exhaust gas recirculation system isless than a first threshold, and where insufficient pressure in the lowpressure exhaust gas recirculation system includes at least whenpressure across the low pressure exhaust gas recirculation system isless than a second threshold.
 2. The method of claim 1 furthercomprising estimating low pressure exhaust gas recirculation flow andhigh pressure exhaust gas recirculation flow based on first and secondintake system flow sensors.
 3. The method of claim 2 wherein said firstintake system flow sensor is upstream of the second intake system flowsensor.
 4. The method of claim 3 where said first intake system flowsensor is upstream of the second end of the low pressure exhaust gasrecirculation system.
 5. The method of claim 3 where said first intakesystem flow sensor is upstream of the turbocharger.
 6. The method ofclaim 3 further comprising adjusting geometry of the turbocharger. 7.The method of claim 6 further comprising adjusting temperature in theintake system by adjusting the first and second valves and the first andsecond throttles.
 8. The method of claim 6 further comprising adjustingtemperature in the intake system by adjusting the first and secondvalves.
 9. A system for a diesel engine having an intake system and anexhaust system, comprising: a turbocharger coupled between the intakeand exhaust systems of the engine; a low pressure exhaust gasrecirculation system with a first end coupled to the exhaust systemdownstream of the turbocharger and a second end coupled to the intakesystem upstream of the turbocharger, said low pressure exhaust gasrecirculation having a first valve coupled in low pressure exhaust gasflow and a first throttle coupled in the intake system; a high pressureexhaust gas recirculation system with a first end coupled to the exhaustsystem upstream of the turbocharger and a second end coupled to theintake system downstream of the turbocharger, said high pressure exhaustgas recirculation having a second valve coupled in high pressure exhaustgas flow and a second throttle coupled in the intake system upstream ofthe first throttle; and a controller including code programmed into acomputer readable storage medium in the controller, the controllerincluding code for adjusting low pressure exhaust gas flow by varyingsaid first valve when sufficient pressure exists across the low pressureexhaust gas recirculation system, and adjusting low pressure exhaust gasflow by varying said first valve and said first throttle otherwise,where sufficient pressure exists across the low pressure system at leastwhen the pressure across the low pressure system is greater than a firstthreshold; code for adjusting high pressure exhaust gas flow by varyingsaid second valve when sufficient pressure exists across the highpressure exhaust gas recirculation system, and adjusting high pressureexhaust gas flow by varying said second valve and said second throttleotherwise, where sufficient pressure exists across the high pressuresystem at least when the pressure across the high pressure system isgreater than a second threshold; and code for coordinating adjustment ofthe first and second valves and first and second throttles to compensatefor interaction between the high and low pressure exhaust gasrecirculation systems.
 10. The system of claim 9 further comprising afirst mass airflow sensor coupled in the engine intake system upstreamof said second end of said low pressure exhaust gas recirculationsystem.
 11. The system of claim 10 further comprising a second massairflow sensor coupled in the engine intake system upstream of saidsecond end of said high pressure exhaust gas recirculation system anddownstream of said second end of said low pressure exhaust gasrecirculation system.
 12. The system of claim 11 wherein said controlleris further configured to estimate and control flows in said low pressuresystem and said high pressure systems in response to at least said firstand second mass airflow sensors.
 13. The system of claim 12 whereinsufficient pressure exists across the low pressure exhaust gasrecirculation system when adjustment of the first valve provides adesired low pressure exhaust gas recirculation flow with the firstthrottled fully opened.
 14. The system of claim 12 wherein sufficientpressure exists across the high pressure exhaust gas recirculationsystem when adjustment of the second valve provides a desired highpressure exhaust gas recirculation flow with the second throttle fullyopened.
 15. The system of claim 14 where said desired high pressureexhaust gas recirculation flow is based on said first and second massairflow sensors.
 16. The system of claim 13 where said desired lowpressure exhaust gas recirculation flow is based on said first andsecond mass airflow sensors.